It open nozzle, but why no spark the plugs? - 2003 Nissan Altima

SOURCE: 2003 Nissan Altima?

Where is the sensor placed on the car?

SOURCE: changing the spark plugs on 2003 altima 2.5L

Not that simple on newer cars, but you do still need those tools.

Here is a good write-up: Changing Plugs on an Altima that will show you the location of the coil packs that must be removed first (9th picture from the bottom) and what they look like.

Doesn't really need to be done until about the 100,000 mile mark. Do not do it while the engine is hot or even warm. Replace with the factory recommended spark plug. Place a little anti-seize on the threads and some dielectric grease on the top. Be sure you torque them down to the proper setting. I believe it is somewhere around 20 ft. lbs., but if you call the Nissan service desk they should be able to tell you for sure.

SOURCE: 2003 nissan altima

First of all, you'll have to clarify which belt it is you're talking about. Is it a SERPENTINE drive belt or a Timing belt? Two totally different belts.
If its a timing belt, you're in luck as Nissan Altimas have timing chains on the engines which shouldn't need replacing for at the very least 100,000 miles. If you're talking about the serpentine drive belt on the other hand, there's really only one way it can go over the pulleys. One side of the belt it grooved, and one side is smooth. There's only one way it can go over all of the pulleys while having the grooved face sitting on grooved pulley surfaces,... should be really easy to figure out.

SOURCE: engine is misfiring. 2.5L 2003

one of the small screws that secure the plates to the shaft of the swirl control system inside of intake manifold mostlikely fell out and wound up in the cylinder of the damged plug causing the damage to the plug.there was a recall by nissan to remedy this by replacing screw with threadlocker.contact your local dealer for info.

SOURCE: 2003 Nissan altima alternator

The alternator is right on top of the 2.5L motor and held on by 2 14mm bolts. To remove the lower bolt (hard to reach), you must remove the coolant bottle and the IPDM fuse board and its metal box/bracket. A breaker bar really helped give enough torque to loosen the bolts. Approach the drive belt from under the front passenger tire. There is a tension adjuster (hard to reach) bolt that loosens the belt and allows you to remove it from the alternator.